WHAT IS A MARINE MAMMAL?

•Member of Class: MAMMALIA

•All possess major adaptations that allow them to live in the water (to a greater or lesser extent)

•Some marine mammals live entirely in the marine environment, others may come on land for part of their lives

•However, all marine mammals derive all (or most) of their food from the marine environment

POLAR BEAR

Ursus maritimus

SEA OTTER

Enhydra lutris

SIRENIANS- Manatees and dugongs

PINNIPEDS- Seals, sealions and walruses

CETACEANS

Whales, dolphins and porpoises

CRETACEOUS PALAEOCENE EOCENE OLIGOCENE

CANIDAE (Dogs)

FELIDAE (Cats)

CARNIVORA

UNGULATA

PERISSODACTYLA (Odd-toed ungulates)

ARTIODACTYLA (Even-toed ungulates)

CETACEA (Whales and dolphins)

PINNIPEDIA (Seals)

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HYDRACOIDEA (Hyraxes)

PROBOSCIDAE (Elephants)

SIRENIAPAENUNGULATA

Whales, dolphins and porpoises are all members of the mammalian order

CETACEAThere are currently 84 (±)

recognised species in the order.

Order: CETACEA

Sub-Order: MYSTICETI

The Baleen or “filter-feeding”

Whales

10 or 13 species

•The Baleen whales all possess hundreds of plates of baleen instead of teeth.

•Baleen is made of keratin and hangs from the upper jaw.

•The fringed baleen plates trap engulfed prey and filter out water.

Order: CETACEA

Sub-Order: ODONTOCETI

The Toothed Whales

69 to 73 species recognised

The sub-order ODONTOCETI is split

into ten families:

CETACEA

Order Sub Orders

Archaeoceti

Mysticeti

Odontoceti

Beaked whales Ziphioidea

Indian river dolphins PlatanistoideaAmazon river dolphin Iniidae

Yangtze river dolphin Lipotidae

Sperm whales PhyseteridaePygmy sperm whales Kogiidae

Franciscana dolphin Pontoporiidae

Beluga & Narwhal Monodontidae

Dolphins Delphinidae

Porpoises Phocoenidae

Cetaceans have adapted to a Cetaceans have adapted to a wide range of aquatic habitatswide range of aquatic habitats

RIVERS, LAKES, LAGOONS AND ESTUARIES: eg River, Irrawaddy and humpback dolphins

INTERTIDAL (mudflats and mangroves): eg bottlenose & humpback dolphins

SUBLITTORAL (continental shelf) – c. 45 miles from coast <200m deep

BATHYAL ZONE (continental slope) to 3,500’ (1,100m): eg beaked whales

ABYSSAL ZONE – flat and low productivity av. 13,000’ (4,000m):

eg sperm whale and beaked whale

• TEMPERATURE: 40oC – humpback dolphins in the Arabian Gulf

-1.9oC – cetaceans in Antarctic

• DEPTH: <5m – river dolphins

2,000m – sperm whales

200 x atmospheric pressure

Cetaceans have adapted to a Cetaceans have adapted to a wide range of aquatic habitatswide range of aquatic habitats

COLD TEMPERATURES• Insulating blubber layer• Counter-current system reduced heat

loss through flukes and finsas blood flows from body gives heat to cooler, parallel blood vessel entering body

HOT TEMPERATURES• Vasodilation (blushing)• Increased blood vessels in skin

TEMPERATURE ADAPTATIONS

• Closable blowhole on top of head

• Fore limbs → flippers • No hind limbs (or minute vestiges)

• No zygapophyses → back bone flexible

• Cartilaginous flukes

• Thick cornea & thick eye mucus• Hydrodynamic (reduced drag)

SWIMMING ADAPTATIONS

HYDRODYNAMICHYDRODYNAMIC

• Low Surface Area: Volume ratio• No hair (facial bristles on some young)

• Skin replaced every 2 hours (keeps smooth surface)

• Genitals and gonads internal• Blubber smoothes contours (tapered shape)

• Shape indicates speed: – Spinner dolphin: long beak (concorde)– Risso’s dolphin: blunt head (jumbo jet)– Sperm whale: square head (submarine)

• Buoyant blubber layer

• Flippers act as hydroplanes (produce lift)

• Porous bones• Fat filled bones (eg mysticeti vertebrae)

• Dense bones (eg rib cages)

• Spermaceti organ –

Waxy spermaceti changes density with temperature - adjustable buoyancy

BOUYANCY CONTROLBOUYANCY CONTROL

• High level of myoglobin (O2 storage)• Blood diverted to essential organs• Retae mirabila: extra circulatory system

→ greater blood volume• High anaerobic tolerance in tissues• Blood storage in spleen – released in

dives• Reduced blood viscosity• Bradycardia (25% in bottlenose

dolphins) and decreased metabolic rate

DIVING ADAPTATIONS

DIVING ADAPTATIONS• Brain and heart most vulnerable to lack of

oxygen

• Cetacean brains operate at O2 concentrations where a human would be unconscious

• High levels of anaerobic respiration in brain at end of dive

• Heart activity decreases (& O2 demand)

• Blood flow fluctuates (high/none) to periodically flush out anaerobic by-products

• High levels of anaerobic respiration

• ‘The Bends’ are caused by dissolved nitrogen being absorbed into the blood stream under high pressure.

• When pressure decreased the dissolved nitrogen come out of solution as tiny bubbles.

• These bubbles can block blood capillaries – causes pain, paralysis etc.

AVOIDING THE BENDS

• Rib cage collapsible & lungs can compress.

• Air squeezed out of lungs and thorax into windpipe.

• Windpipe thickened, does not absorb air (or dissolved nitrogen).

• Rapid transfer of nitrogen from blood into lungs

• Some absorption of nitrogen in mucus

• Reduced circulation of blood to muscles – less risk or capillary block

AVOIDING THE BENDS

OSMOREGULATORYADAPTATIONS

• High in take of salt

• Saline surroundings (high OP) absorbs water from cetaceans

• Specialised globular kidney (reniculi) looks like

bunch of grapes

• High surface area for filtration

• Water produced by fat metabolism

• Seawater desalinated by kidney

• Very concentrated urine

• Voluntary breathing – must be conscious to open blow hole.

• A few species sleep as such:– Right whales (very buoyant)– Sperm whales (float – do not have to breathe

for hours at a time)

• Duplication of brain function – part of brain can sleep while another part awake.

SLEEP

HEARING• Odontocete vocalisations produced in

windpipe• Focussed by fatty melon (acts like a lens)• In water sound would reach dolphin ears

simultaneously – would not be able to pin-point direction.

• Sound received through lower jaw.• Two halves of lower jaw separated by

insulating tissue.• Sound travels through jaw and vibrations

passed to inner ear.

MIGRATIONS

• Many large whale species migrate from polar region (to feed) to tropics (to breed)

• Accumulation of stored fat before start• Vast distances – up to 50% weight loss• High speed: blue and fin whales

17kmph for 3,700 km.

Why?

• Breed in warm waters as weather calmerweather calmer for calves.

• Calves loose heatCalves loose heat easily as have a high surface area: volume ratio

BUT – half of humpbacks, belugas, bowheads, orcas and narwhals never migrate (always polar)

• Escape predatorsEscape predators (killer whales) – although in tropics other predators (sharks)

• Possible behavioural relicbehavioural relic from when breeding and mating grounds closer -

unlikely

MIGRATIONS

• Seawater is a spermicide – water tight valves

• Prehensile penises• Some polygynous (eg orca, dominant male)• Almost all cetaceans promiscuous

(multimate polygynandry)• Male competition-aggressionaggression (eg humpback - fin slapping)-vocalisationsvocalisations (eg humpback song – territories)-sperm competitionsperm competition (on average testes 25x larger

than expected - dusky dolphins testes relatively 100x larger than humans)

REPRODUCTION

• Most species sexually mature after 5-6 years

• However, may be denied mating by more dominant animals for several years

• Always single calves are born

• Some species have calving seasons, some species give birth year round

• Usually 2-3 year calving interval

• Low reproductive rateLow reproductive rate

REPRODUCTION

• Calves are born in water and pushed to surface.

• Stay with mothers for six months to 10 years or more

• Lactation via retractable nipples• Milk has very high fat content (40% - only

4% in cow milk)• Calves may suckle for several years even

after weaning (- bonding)• Females go through menapause

REPRODUCTION

• Harbour porpoise – 15 years• Bottlenose dolphin – 50 years• Killer whale – 90+ years

• But only 20-25 years in captivity• Blue whales - 100+ years• Bowhead whales – 218 years +

Long life cycles and low reproductive rate Long life cycles and low reproductive rate means that the recovery of depleted means that the recovery of depleted

populations is slowpopulations is slow

LONGEVITY

Similar to W. Indian manatee but: blunter snout

more protruding eyes

more slender body

West Indian manatee

West African manatee

Cetacean-like tail

No nails on flippers

<3m long

Dugong

Tusks

Amazonian Manatee

Totally marine

Totally freshwaterWhite patches

SIRENIAN ADAPTATIONS

All sirenians are totally aquatic

- like cetaceans but unlike otters & pinnipeds

Herbivorous

- unique amongst marine mammals

Various adaptations to aquatic environment

AQUATIC ADAPTATIONS• No pelvic limbs• Reduced/paddle-like pectoral fins• Fusiform (streamlined/spindle-shaped) body• Very large - reduced heat loss• Thick impermeable skin - reduced water loss• Lobular kidney - improved water extraction/salt

excretion• Nostrils on top of muzzle• Thick heavy bones (pachyosteosclerotic) – ballast• Lungs dorsal with two horizontal diaphragms –

buoyancy control

MANTEE ECOLOGY

• Nutritionally poor diet• Metabolic rate 20-30 % lower than expected• Primarily plant diet-some times eat fish captured in nets & tunicates

• Predation low: crocodiles/alligators and sharks

• Most mortality: coldred tidesboat collisionby-catch

Pinniped = pinna (wing) + ped (foot)

Comprise 25% of the 115 marine mammal species

More than 50 million pinnipeds worldwide

Order: PINNIPEDIA

Family: OTARRIDAE

Eared sealsFur seals (9 species)

Sealions (5 species)

Otarrids all have certain characteristics in common

Visible external ears

Hinged hind flippers

= mobility on landUsed fore flippers like wings – flying through the water

Order: PINNIPEDIA

Family: OBENIDAE

Walruses1 species

Order: PINNIPEDIA

Family: PHOCIDAE

True seals

Northern seals (Phocinae) 10 species

Southern seals (Monachinae) 9 species

Phocids also have certain characteristics in common

No external ears

Hind flippers not hinged = less mobility on land

Use hind flippers for propulsion (side to side)

Fore flippers used to direct

Although they feed in the sea all seals give birth on land

They “haul up” onto beaches to breed

Seal pups are very vulnerable so they grow and are weaned quickly

Seal milk is 30-60% fat (vs 4% in cow milk)

Pups gain weight & a thick blubber layer quickly

AQUATIC ADAPTATIONS

• Webbed toes and fore limbs have developed into paddle-like pectoral fins

• Fusiform (streamlined/spindle-shaped) body

• Thick blubber layer - reduced heat loss• Insulating hair layer (especially in fur

seals)• Flippers enervated with blood vessels –

radiate heat when on land to avoid overheating

AQUATIC ADAPTATIONS

• Counter current system to prevent heat loss via limbs in water

• Nostrils on top of muzzle

• Sensory vibrissae (whiskers) help to detect movement in water

• Reflecting layer or TEPETUM in eye- allows low light vision

DIVING ADAPTATIONS

• Can store large amount of oxygen in blood and tissues

• Can withstand high concentrations of lactic acid (product of anaerobic respiration)

• Can reduce their heart rate (BRADYCARDIA) and metabolic rate – reduces rate oxygen is used up

• Lungs collapse when they dive – no absorption of nitrogen under pressure – no “BENDS”